A photovoltaic cell converts the energy of sunlight into electricity by the photovoltaic effect. Assemblies of photovoltaic cells are used to make photovoltaic modules or solar panels. Most currently available photovoltaic cells are made from bulk materials such as crystalline silicon or polycrystalline silicon. Photovoltaic cells can also be made of thin film layers deposited on a substrate. Thin film photovoltaic cells reduce the amount of material required thus reducing material cost compared to bulk photovoltaic cells. Thin film photovoltaic cells are becoming increasingly popular due to their low cost, flexibility, light weight, and ease of integration.
Reliability has been a major concern for thin film photovoltaic modules in the solar energy industry. Quality control tests on some conventional thin film photovoltaic modules under damp heat have shown fast performance degradation as a function of test time manifested as an increase in series resistance (RS) and a decrease in position at maximum power point (PMPP). The cause of the degradation is determined to be due to delamination of the front conductive layer as a result of TCO corrosion after being exposed to humidity. One possible mechanism of the TCO corrosion is due to sodium reduction reactions occurring at the glass-TCO interface upon exposure to moisture in the surrounding environment. Another possible mechanism is due to the etching process caused by fluorine ions in fluorine tin oxide (FTO) upon exposure to moisture in the surrounding environment. Various wet encapsulation methods, including wrap sealant in the module frame, metal tape around the edges of the module, glass-glass bonding, and edge sealant, have been developed to prevent the TCO corrosion. Other methods, such as creating a diffusion barrier for sodium ions, have also been used. However, these methods have not been effective in solving the corrosion problem. Negative grounding is also used to lesson the corrosion problem. This method however is not cost effective because transformerless inverters cannot be used.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.